In recent years, a Single-Mode type (SM type) glass optical fiber is widely used for a long-distance trunk line, and it is targeted to build an information network by using this kind of optical fiber. By the way, a core diameter of the SM type optical fiber is 5 to 10 microns, which is extremely thin. Therefore, means for connecting and branching the optical fiber with high accuracy is needed in setting in the optical fiber.
Therefore, a high-accuracy optical fiber connector 1 shown in FIG. 4 has been used, for example. In the optical fiber connector 1, a minute aspherical lens 8 having a lens surface 7 of predetermined shape is fitted into an edge portion of a connector body 2 while having a space portion 6 between the aspherical lens and a tip of a fiber 4 of an optical fiber wire 3 buried in a resin 5, and the aspherical lens 8 changes emitted light from the tip of the fiber 4 of the optical fiber wire 3 into a parallel light (see dotted lines in FIG. 4).
The core diameter of the optical fiber wire 3 is 5 to 10 microns, which is extremely thin. Therefore, the aspherical lens 8 whose diameter is about 1 mm is usually used. However, in the case where the aspherical lens 8 having a minute diameter of about 1 mm is fitted into the connector body 2, it is very difficult to align an optical axis of the optical fiber wire inserted in the connector body 2 and an optical axis of the aspherical lens 8. There is such a problem that misalignment of optical axes decreases quality and reliability and increases a cost of products.
To solve the problems, the applicant of the present application disclosed a high-accuracy optical fiber connector which is applicable to an optical fiber having a minute core diameter such as the SM type optical fiber and also disclosed its production method, in Japanese Unexamined Patent Application Publication No. 15448/1997 (Tokukaihei 9-15448, published on Jan. 17, 1997).
According to the production method, first, inserted into a connector body 22 is a fiber 24 led out from an edge portion of an optical fiber wire 23 having the fiber 24 of a small diameter. Then, an ultraviolet hardening resin 26 is injected and filled in a front portion of the edge portion where the fiber is led out, as shown in FIG. 5(a). Next, a transfer body 20 having a lens transfer surface 21 is pressed against the ultraviolet hardening resin 26, the ultraviolet rays UV are irradiated through the transfer body 20 as shown in FIG. 5(b) to harden the ultraviolet hardening resin 26. After that, the lens transfer surface 21 is transferred to a surface of the ultraviolet hardening resin 26 by the lens transfer surface 21.
However, according to the production method disclosed in the Japanese Unexamined Patent Application Publication No. 15448/1997, an special jig such as the transfer body 20 having the lens transfer surface 21 is required in order to form a lens surface on a surface of the ultraviolet hardening resin 26 which is injected and filled in the edge portion of the connector body 22. In addition, the production method requires a step to press the transfer body 20 against the surface of the ultraviolet hardening resin 26. Therefore, the problem here is that its production steps become complicated.
To solve the problem, the inventor of the present application disclosed a production method for an optical fiber connector in Japanese Unexamined Patent Application Publication No. 23015/2002 (Tokukai 2002-23015, published on Jan. 23, 2002). The following description deals with the production method with reference to FIGS. 6(a) through 6(c). First, in order to form an pre-lens, one kind of the ultraviolet hardening resin 26 is injected into a resin-injection portion 29 of the connector body 22 by using a resin injector 30 until the ultraviolet hardening resin 26 protrudes at the top of the connector body 22. Next, ultraviolet rays are irradiated to the resin to harden while a wave front measurement is performed, and finally a lens surface (lens) is formed.
However, according to the production method for the lens disclosed in the Japanese Unexamined Patent Application Publication No. 23015/2002, when the resin is hardened by the irradiation of the ultraviolet rays while the wave front measurement is performed, volume shrinkage (polymerization shrinkage) of the resin occurs greatly, so that a lens length (i.e. height of the ultraviolet hardening resin) becomes short after the resin is hardened. Therefore, in order to harden the resin, it is required to recognize an amount of the volume shrinkage in advance. However, it is difficult to estimate the amount of the volume shrinkage of the hardened resin. For this reason, even though the resin is hardened while the wave front measurement is performed, a desired lens shape cannot be obtained. Specifically speaking, such large volume shrinkage causes a large difference between the pre-lens shape and the hardened lens shape. Therefore, it is difficult to control the lens shape, and a light collection property of the lens obtained is low. In addition, air bubbles are also generated inside the resin. This is also one reason of the volume shrinkage.
As above, according to the production method for the lens disclosed in the above publication, a reproducibility of the lens surface is low because of the volume shrinkage, air bubbles generated inside the resin, or the like reason, and it is difficult to control the lens surface shape with high accuracy. As a result, a problem arises where it is impossible to obtain the lens having a high light collection property.
Therefore, what is desired is the production method by which the lens surface shape is easily fine adjusted and the optical lens is improved in the light collection characteristic.
The present invention was made to solve the above problems, and an object of the present invention is to provide the production method for the optical lens and the production method for the optical fiber connector by which influences by the volume shrinkage of the resin are decreased and the formation of the lens surface can be controlled with high accuracy.